It’s happening again. When the weather gets warm, we start getting these tiny, annoying fruit flies (you know, the ones with the red eyes) in the house. I can’t enjoy my glass of wine anymore because they’re always hovering over it. What causes them to come out when it gets hot?–W. B., Atkinson, NH

Blame the Flies on the Fresh Produce

It’s not the weather directly that causes the fruit flies. It’s the fresh produce that appears everywhere in mid-summer, thanks to the warm weather. Fruit fly larvae feed on decaying organic materials – that means anything from an overripe peach, to a rotting potato, to the sludge in the bottom of a dirty garbage can. Even more than that though, the adult flies are attracted to the yeasty smells that indicate fermentation. That’s why they like your wine and why they can be serious pests in breweries or in wine production.

There’s a Reason Why They Are Called Fruit Flies

Like most of us, you probably take advantage of the many produce stands and farmers’ markets offering fruits and vegetables. If you leave a bowl of ripe fruit sitting on your table, or boxes of tomatoes in the pantry, you are calling fruit flies. Or, maybe you have your own fruit trees or your own vegetable garden. If you don’t routinely pick up fallen and rotting fruits and vegetables in your yard, fruit flies will find them and lay their eggs in the produce. Outdoor fruit flies can then find their way inside.

If Not the Produce, Then What?

If you’ve taken care of the ripe fruit in your home by eating it or storing it covered, and you still have fruit flies after a period of time, then you might have a breeding fruit fly population somewhere else. Fruit fly larvae can develop successfully in many things. These are some other sites where you can find fruit flies:

• Residues or spilled vinegary or yeasty foods like beer, wine, vinegar, ketchup, or cider. Check for not-quite-empty cans or bottles in the recycling bin
• Garbage cans that have accumulated semi-liquid goo in the bottom. Look underneath plastic trash can liners for overlooked spills
• Drip pans underneath refrigerators, air conditioners, hot water heaters, etc. that have accumulated organic scum
• Dirty trash compactors or garbage disposals
• Slimy potted plant saucers
• Scummy wash water left in buckets or sinks
• Dirty floor drain traps
• Potato or onion bins. Look for rotting produce on the bottom

By Adam Chamness from Kochi City, Japan (Fruit Fly (macro)) [CC-BY-SA-2.0], via Wikimedia Commons